Positive electrode material coated with composite oxide, preparation method therefor, and use thereof

Abstract

A positive electrode material coated with a composite oxide, a preparation method therefor, and the use thereof. The positive electrode material comprises an inner core and a coating layer on the surface of the inner core; the chemical general formula for the inner core is: NabNixFeyMnzM1-x-y-zO2, wherein 0.4 ≤ b ≤ 1.2, 0.10 ≤ x ≤ 0.50, 0.10 ≤ y ≤ 0.50, 0.10 ≤ z ≤ 0.50; the coating layer comprises a composite oxide, and the composite oxide comprises two or more metal elements. The positive electrode material is coated with the composite oxide, which significantly improves the conductivity and stability of the positive electrode material, reduces contact between the positive electrode material and an electrolyte, inhibits the occurrence of side reactions, and improves the cycle performance of the material.

Description

A composite oxide-coated positive electrode material and its preparation method and application Technical Field

[0001] The present application belongs to the field of battery technology and relates to a positive electrode material coated with a composite oxide and a preparation method and application thereof. Background Art

[0002] With the continuous advancement of science and technology, people's demand for energy is increasing. However, the use of traditional fossil fuels can cause serious environmental pollution. Therefore, clean, renewable new energy sources that can replace traditional fossil fuels have become a research hotspot. In recent years, the supply of lithium-ion battery materials has exceeded demand, and the price of raw materials has continued to rise. Lithium resources are low in surface content and unevenly distributed. From the perspective of long-term energy development, abundant, safe, and low-cost raw materials are required. Due to the similar physical and chemical properties of sodium and lithium and its abundant reserves, sodium-ion batteries are expected to replace lithium-ion batteries and have great application potential in electric motorcycles, low-speed electric vehicles, and large-scale energy storage.

[0003] However, sodium-ion batteries face significant challenges during the charge and discharge process, including severe phase structure transitions, slow diffusion kinetics, and interfacial degradation. Layered transition metal oxide cathode materials, with their compact crystal structure, low cost, and ease of synthesis, are a promising class of cathode materials for sodium-ion batteries. Modifications to sodium-ion batteries primarily involve coating and doping the cathode materials. There are four main types of coating materials for sodium-ion battery cathode materials: metal oxides, non-metallic element coatings, sodium / lithium fast ion conductors, and organic / conductive polymers.

[0004] For example, CN 116759570A discloses a sodium-ion battery cathode material, a preparation method thereof, a cathode, and a sodium-ion battery. The sodium-ion battery cathode material comprises a sodium-containing layered oxide and a coating layer coated on the surface of the sodium-containing layered oxide. The coating layer comprises a polyanionic sodium-containing compound having a NASICON crystal structure, and the polyanionic sodium-containing compound comprises sodium and a transition metal element. The total residual sodium content of the sodium-ion battery cathode material is 2.4 to 4.2 wt% of the mass of the sodium-ion battery cathode material. The coating layer having the NASICON fast-conducting sodium ion conductor structure improves the surface stability of the material, ultimately enabling the sodium-ion battery using this sodium-ion battery cathode material to exhibit excellent electrical properties such as rate capability and cycle performance.

[0005] While different types of coating materials for sodium-ion battery cathode materials each have their own advantages, they also have their own shortcomings. The means and effects of doping and coating modification are limited, and the resulting coating structures cannot achieve uniform and stable coating effects. Furthermore, the coatings typically form relatively stable ionic conductors on the surface, but with poor conductivity and significant material polarization.

[0006] Based on the above research, it is necessary to provide a positive electrode material coated with a composite oxide, wherein the surface coating layer of the positive electrode material is uniform, which can reduce the contact between the positive electrode material and the electrolyte, inhibit the occurrence of side reactions, improve the cycle performance of the material, and at the same time improve the problem of poor conductivity of the material itself.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] The purpose of this application is to provide a positive electrode material coated with a composite oxide, a preparation method and an application thereof, wherein the positive electrode material is coated with the composite oxide, which significantly improves the conductivity and stability of the positive electrode material, reduces the contact between the positive electrode material and the electrolyte, inhibits the occurrence of side reactions, and improves the cycle performance of the material.

[0010] To achieve this goal, this application adopts the following technical solutions:

[0011] In the first aspect, the present application provides a positive electrode material coated with a composite oxide, wherein the positive electrode material coated with the composite oxide comprises a core and a coating layer on the surface of the core, wherein the chemical formula of the core is Na b Ni x Fe y Mn z M 1-x-y-z O2, wherein 0.4≤b≤1.2, 0.10≤x≤0.50, 0.10≤y≤0.50, 0.10≤z≤0.50, M includes any one or a combination of at least two of Li, Cu, Al, Mg, Zn, Sn, Ti, Zr, Sr, Sb, Nb, Ba, Cr, Mo, Y, Ca, Rb, Cs, Ce, Ta, V, Sc, B, V, Co, La, Ru or W, and the coating layer includes a composite oxide, and the composite oxide includes two or more metal elements.

[0012] The positive electrode material described in the present application is coated with a composite oxide containing two or more metal elements. The composite oxide has high stability and conductivity, which can not only prevent the positive electrode material from getting damp, resist the erosion of the electrolyte, and inhibit interfacial side reactions, but also improve the problem of poor conductivity of the material itself, thereby further improving the electrochemical performance of sodium batteries. In addition, the core of the present application is doped with elements to expand the ion transmission channel, stabilize the structure of the material, and further improve the electrochemical performance of the battery.

[0013] The chemical formula of the core is Na b Ni x Fe y Mn z M 1-x-y-z O2, wherein 0.4≤b≤1.2, for example, it can be 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0, 0.10≤x≤0.50, for example, it can be 0.2, 0.4 or 0.5, 0.10≤y≤0.50, for example, it can be 0.2, 0.4 or 0.5, 0.10≤z≤0.50, for example, it can be 0.2, 0.4 or 0.5, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] In one embodiment, the composite oxide comprises zinc aluminum oxide.

[0015] The composite oxide of the present application is zinc aluminum oxide. Compared with other composite metal oxides, Zn can improve the conductivity of the material, and Al can improve the cycle performance of the material. The synergistic effect of the two can greatly improve the material performance.

[0016] In one embodiment, the particle size D50 of the core is 3-14 μm, for example, 5 μm, 8 μm, 10 μm or 14 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0017] In one embodiment, the thickness of the coating layer is 0.2-2 μm, for example, 0.2 μm, 0.5 μm, 1 μm, 1.5 μm or 2 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0018] The thickness of the coating layer described in this application will affect the battery performance. If the coating layer is too thick, the energy density and rate performance of the material will be reduced. If the coating layer is too thin, the cycle stability will deteriorate.

[0019] In a second aspect, the present application provides a method for preparing a positive electrode material coated with a composite oxide as described in the first aspect, the preparation method comprising the following steps:

[0020] (1) mixing a nickel-iron-manganese metal salt solution, an M salt solution, a precipitant solution, and a complexing agent solution to perform a coprecipitation reaction to obtain a core precursor material;

[0021] (2) After obtaining the core precursor material of step (1), stopping the feeding of nickel-iron-manganese metal salt solution and M salt solution, introducing the coating source solution, and allowing the coating source solution to continue to coprecipitate with the precipitant solution and the complexing agent solution to obtain the positive electrode precursor material; the coating source solution includes two or more metal elements;

[0022] (3) Mixing and sintering the sodium source with the positive electrode precursor material in step (2) to obtain the positive electrode material coated with the composite oxide.

[0023] The present application performs doping during the co-precipitation process of preparing the precursor, so that the doped precipitate phase formed in situ is evenly distributed, and uniform mixing at the atomic level can be achieved, successfully introducing the doping elements into the crystal lattice of the positive electrode material, expanding the ion transmission channel, and stabilizing the material structure; in addition, a mixed coating layer of hydroxide is coated on the surface by the co-precipitation method. The coating method is simple and easy to operate, and a coating layer of a composite oxide is formed after subsequent sintering, which can prevent the positive electrode material from getting damp, resist the erosion of the electrolyte, and inhibit interfacial side reactions. In addition, the composite oxide formed in situ has excellent conductivity and stability, which can further improve the electrochemical performance of sodium batteries.

[0024] In one embodiment, the total metal ion concentration in the nickel-iron-manganese metal salt solution of step (1) is 0.6-5 mol / L, for example, it can be 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L or 5 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] In one embodiment, the nickel-iron-manganese metal salt solution in step (1) is obtained by mixing nickel salt, manganese salt, iron salt and water, wherein the nickel salt includes any one of nickel sulfate, nickel chloride or nickel nitrate or a combination of at least two; the iron salt includes any one of ferrous sulfate, ferrous chloride or ferrous nitrate or a combination of at least two; and the manganese salt includes any one of manganese sulfate, manganese chloride or manganese nitrate or a combination of at least two.

[0026] In one embodiment, the concentration of the M salt solution in step (1) is 0.05-2 mol / L, for example, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L, but is not limited to the values ​​listed, and other values ​​not listed within the numerical range are also applicable.

[0027] In one embodiment, the concentration of the precipitant solution in step (1) is 1-10 mol / L, for example, 2 mol / L, 5 mol / L, 8 mol / L or 10 mol / L, and the concentration of the complexing agent solution is 2-15 mol / L, for example, 3 mol / L, 5 mol / L, 8 mol / L, 10 mol / L, 12 mol / L or 15 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] In one embodiment, the nickel-iron-manganese metal salt solution, M salt solution, precipitant solution and complexing agent solution of step (1) are simultaneously introduced into the base liquid to carry out a co-precipitation reaction.

[0029] In one embodiment, the base solution is obtained by stirring and mixing water, a precipitant solution and a complexing agent solution.

[0030] In one embodiment, the pH of the base solution is 9-12, for example, 9, 10, 11 or 12, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] In one embodiment, the temperature of the coprecipitation reaction in step (1) is 20-80°C, for example, 30°C, 50°C, 70°C or 80°C, and the pH is maintained in the range of 7-11, which means that the minimum pH is above 7, for example, 7, 7.5 or 8, and the maximum is below 11, for example, 11, 10.5 or 10, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] In one embodiment, the coprecipitation reaction in step (1) is stopped when the particle size D50 of the product particles is 3-14 μm, for example, 3 μm, 5 μm, 7 μm, 10 μm or 14 μm, to obtain the core precursor material.

[0033] In one embodiment, the coating source solution in step (2) includes an aluminum salt solution and a zinc salt solution.

[0034] In one embodiment, the molar ratio of zinc ions in the zinc salt solution to aluminum ions in the aluminum salt solution is (1-4):1, for example, 1:1, 2:1, 3:1 or 4:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] When the molar ratio of zinc ions to aluminum ions described in the present application is within the above range, the two can play a synergistic role. If it is not within the above range, such as when the zinc ions are too few compared to the aluminum ions, the rate performance deteriorates. If the zinc ions are too many compared to the aluminum ions, the cycle performance is greatly reduced.

[0036] In one embodiment, the concentration of the zinc salt solution is 0.5-4 mol / L, for example, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L or 4 mol / L, and the concentration of the aluminum salt solution is 0.1-2.5 mol / L, for example, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L or 2.5 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] In one embodiment, the coprecipitation reaction in step (2) is stopped after the particle size D50 of the product particles increases by 0.2-2 μm compared to the particle size D50 of the product particles in step (1), for example, it can be 0.2 μm, 0.5 μm, 1 μm, 1.5 μm or 2 μm.

[0038] In one embodiment, the temperature of the coprecipitation reaction in step (2) is 30-70°C, for example, 30°C, 40°C, 60°C or 70°C, and the pH is maintained in the range of 7-10, which means that the minimum pH is above 7, for example, 7, 7.5 or 8, and the maximum is below 10, for example, 10, 9.5 or 9, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] After the coprecipitation reaction in step (2) of the present application is completed, aging is performed, and after aging, centrifugal washing is performed using alkaline solution and water.

[0040] In one embodiment, the sintering in step (3) includes a primary sintering and a secondary sintering performed sequentially, the temperature of the primary sintering is 450-600°C, for example, 450°C, 500°C, 550°C or 600°C, and the time is 4-6h, for example, 4h, 5h or 6h, the temperature of the secondary sintering is 750-1200°C, for example, 750°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C, and the time is 10-25h, for example, 10h, 15h, 20h or 25h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0041] In one embodiment, the sintering in step (3) is performed under an oxygen atmosphere.

[0042] As an optional technical solution of the preparation method described in this application, the preparation method comprises the following steps:

[0043] (1) introducing a nickel-iron-manganese metal salt solution, an M salt solution, a precipitant solution, and a complexing agent solution into a base solution having a pH of 9-12 in parallel to perform a coprecipitation reaction, wherein the coprecipitation reaction temperature is 20-80° C., the pH is maintained in the range of 7-11, and the coprecipitation reaction is stopped when the particle size D50 of the product particles is 3-14 μm to obtain a core precursor material;

[0044] In the nickel-iron-manganese metal salt solution, the total metal ion concentration is 0.6-5 mol / L, the concentration of the M salt solution is 0.05-2 mol / L, the concentration of the precipitant solution is 1-10 mol / L, and the concentration of the complexing agent solution is 2-15 mol / L;

[0045] (2) After obtaining the core precursor material of step (1), the feeding of nickel-iron-manganese metal salt solution and M salt solution is stopped, and aluminum salt solution and zinc salt solution are introduced to allow the aluminum salt solution and zinc salt solution to continue to undergo coprecipitation reaction with the precipitant solution and the complexing agent solution, wherein the temperature of the coprecipitation reaction is 30-70° C., and the pH is maintained in the range of 7-10. After the coprecipitation reaction is carried out until the particle size D50 of the product particles is 0.2-2 μm larger than the particle size D50 of the product particles of step (1), the reaction is stopped to obtain the positive electrode precursor material;

[0046] The concentration of the zinc salt solution is 0.5-4 mol / L, and the concentration of the aluminum salt solution is 0.1-2.5 mol / L;

[0047] (3) Mixing the sodium source with the positive electrode precursor material of step (2), and then sintering the mixture at a temperature of 450-600°C for 4-6 hours in an oxygen atmosphere, and then sintering the mixture at a temperature of 750-1200°C for 10-25 hours to obtain the positive electrode material coated with the composite oxide.

[0048] In a third aspect, the present application provides a sodium ion battery, which comprises a positive electrode material coated with a composite oxide as described in the first aspect.

[0049] Compared with the prior art, this application has the following beneficial effects:

[0050] By coating the positive electrode material with a composite oxide containing two or more metal elements, the present application can not only prevent the positive electrode material from getting damp, resist the erosion of the electrolyte, and inhibit the side reactions at the interface, but also improve the problem of poor conductivity of the material itself, thereby further improving the electrochemical performance of sodium batteries; in addition, by doping elements in the core of the present application, the ion transmission channel is expanded, the structure of the material is stabilized, and the electrochemical performance of the battery is further improved.

[0051] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0052] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0053] Example 1

[0054] This embodiment provides a positive electrode material coated with a composite oxide, which includes a core and a coating layer on the surface of the core, wherein the chemical formula of the core is Na 0.67 Ni 0.32 Fe 0.33 Mn 0.32 Mg 0.03 O2, the coating layer is zinc aluminum oxide, the particle size D50 of the core is 8 μm, and the thickness of the coating layer is 1 μm;

[0055] The preparation method of the positive electrode material coated with the composite oxide comprises the following steps:

[0056] (1) Under nitrogen protection, nickel-iron-manganese metal salt solution, M salt solution, precipitant solution and complexing agent solution are simultaneously introduced into a base liquid with a pH of 10 to perform a coprecipitation reaction, wherein the temperature of the coprecipitation reaction is 40° C. and the pH is maintained in the range of 7-11. The coprecipitation reaction is stopped when the particle size D50 of the product particles is 8 μm to obtain a core precursor material;

[0057] The nickel-iron-manganese metal salt solution has a total metal ion concentration of 2 mol / L, the M salt solution is a magnesium sulfate solution with a concentration of 0.5 mol / L, the precipitant solution is a sodium hydroxide solution with a concentration of 10 mol / L, and the complexing agent solution is an ammonia solution with a concentration of 8 mol / L; the base solution is obtained by uniformly mixing and stirring pure water, the precipitant solution, and the complexing agent solution;

[0058] (2) After obtaining the core precursor material of step (1), the feeding of nickel-iron-manganese metal salt solution and M salt solution is stopped, and aluminum salt solution and zinc salt solution are introduced to allow the aluminum salt solution and zinc salt solution to continue to undergo coprecipitation reaction with the precipitant solution and the complexing agent solution, wherein the temperature of the coprecipitation reaction is 40° C. and the pH is maintained in the range of 7-10. After the coprecipitation reaction is carried out until the particle size D50 of the product particles increases by 1 μm compared with the particle size D50 of the product particles of step (1), the reaction is stopped to obtain the positive electrode precursor material;

[0059] The zinc salt solution is a zinc sulfate solution with a concentration of 2 mol / L, the aluminum salt solution is an aluminum sulfate solution with a concentration of 0.6 mol / L, and the molar ratio of zinc ions in the zinc salt solution to aluminum ions in the aluminum salt solution is 1.67:1;

[0060] (3) Sodium carbonate is mixed with the positive electrode precursor material of step (2), and then sintered at 500° C. for 5 h in an oxygen atmosphere and then sintered at 1000° C. for 15 h to obtain the positive electrode material coated with the composite oxide.

[0061] Example 2

[0062] This embodiment provides a positive electrode material coated with a composite oxide, which includes a core and a coating layer on the surface of the core, wherein the chemical formula of the core is Na 0.67 Ni 0.5 Fe 0.2 Mn 0.25 Ti 0.05 O2, the coating layer is zinc aluminum oxide, the particle size D50 of the core is 3 μm, and the thickness of the coating layer is 0.2 μm;

[0063] The preparation method of the positive electrode material coated with the composite oxide comprises the following steps:

[0064] (1) Under nitrogen protection, a nickel-iron-manganese metal salt solution, a Ti salt solution, a precipitant solution, and a complexing agent solution are simultaneously introduced into a base liquid having a pH of 12 to perform a coprecipitation reaction. The temperature of the coprecipitation reaction is 50° C., and the pH is maintained in the range of 7-11. The coprecipitation reaction is stopped when the particle size D50 of the product particles is 3 μm, thereby obtaining a core precursor material.

[0065] The nickel-iron-manganese metal salt solution has a total metal ion concentration of 4 mol / L, the Ti salt solution is a titanium sulfate solution with a concentration of 1 mol / L, the precipitant solution is a sodium hydroxide solution with a concentration of 2 mol / L, and the complexing agent solution is ammonia water with a concentration of 15 mol / L; the base liquid is obtained by uniformly mixing and stirring pure water, the precipitant solution, and the complexing agent solution;

[0066] (2) After obtaining the core precursor material of step (1), the feeding of nickel-iron-manganese metal salt solution and Ti salt solution is stopped, and aluminum salt solution and zinc salt solution are introduced to allow the aluminum salt solution and zinc salt solution to continue to undergo coprecipitation reaction with the precipitant solution and the complexing agent solution, wherein the temperature of the coprecipitation reaction is 50° C. and the pH is maintained in the range of 7-10. After the coprecipitation reaction is carried out until the particle size D50 of the product particles increases by 0.2 μm compared with the particle size D50 of the product particles of step (1), the reaction is stopped to obtain the positive electrode precursor material;

[0067] The zinc salt solution is a zinc sulfate solution with a concentration of 0.5 mol / L, the aluminum salt solution is an aluminum sulfate solution with a concentration of 0.25 mol / L, and the molar ratio of zinc ions in the zinc salt solution to aluminum ions in the aluminum salt solution is 1:1;

[0068] (3) Sodium carbonate is mixed with the positive electrode precursor material of step (2), and then sintered at 600° C. for 4 h and then sintered at 1200° C. for 10 h in an oxygen atmosphere to obtain the positive electrode material coated with the composite oxide.

[0069] Example 3

[0070] This embodiment provides a positive electrode material coated with a composite oxide, which includes a core and a coating layer on the surface of the core, wherein the chemical formula of the core is Na 0.67 Ni 0.32 Fe 0.33 Mn 0.32 Mg 0.03 O2, the coating layer is zinc aluminum oxide, the particle size D50 of the core is 14 μm, and the thickness of the coating layer is 2 μm;

[0071] The preparation method of the positive electrode material coated with the composite oxide comprises the following steps:

[0072] (1) Under nitrogen protection, nickel-iron-manganese metal salt solution, M salt solution, precipitant solution and complexing agent solution are simultaneously introduced into a base liquid with a pH of 9 to perform a coprecipitation reaction, wherein the coprecipitation reaction temperature is 60° C. and the pH is maintained in the range of 7-11. The coprecipitation reaction is stopped when the particle size D50 of the product particles is 14 μm to obtain a core precursor material;

[0073] The nickel-iron-manganese metal salt solution has a total metal ion concentration of 2 mol / L, the M salt solution is a magnesium sulfate solution with a concentration of 0.5 mol / L, the precipitant solution is a sodium hydroxide solution with a concentration of 10 mol / L, and the complexing agent solution is an ammonia solution with a concentration of 8 mol / L; the base solution is obtained by uniformly mixing and stirring pure water, the precipitant solution, and the complexing agent solution;

[0074] (2) After obtaining the core precursor material of step (1), the feeding of nickel-iron-manganese metal salt solution and M salt solution is stopped, and aluminum salt solution and zinc salt solution are introduced to allow the aluminum salt solution and zinc salt solution to continue to undergo coprecipitation reaction with the precipitant solution and the complexing agent solution, wherein the temperature of the coprecipitation reaction is 60° C. and the pH is maintained in the range of 7-10. After the coprecipitation reaction is carried out until the particle size D50 of the product particles increases by 2 μm compared with the particle size D50 of the product particles of step (1), the reaction is stopped to obtain the positive electrode precursor material;

[0075] The concentration of the zinc salt solution is 4 mol / L, the concentration of the aluminum salt solution is 0.5 mol / L, and the molar ratio of zinc ions in the zinc salt solution to aluminum ions in the aluminum salt solution is 4:1;

[0076] (3) Sodium carbonate is mixed with the positive electrode precursor material of step (2), and then sintered at 450° C. for 6 h and then sintered at 750° C. for 25 h in an oxygen atmosphere to obtain the positive electrode material coated with the composite oxide.

[0077] Example 4

[0078] This embodiment provides a positive electrode material coated with a composite oxide. The positive electrode material coated with a composite oxide is the same as that in Example 1 except that in the preparation method, the coprecipitation reaction in step (2) is stopped after the particle size D50 of the product particles is 0.05 μm larger than the particle size D50 of the product particles in step (1), so that the obtained positive electrode material coated with a composite oxide is adaptively changed.

[0079] Example 5

[0080] This embodiment provides a positive electrode material coated with a composite oxide. The positive electrode material coated with a composite oxide is the same as that in Example 1 except that in the preparation method, the coprecipitation reaction in step (2) is stopped after the particle size D50 of the product particles is 3 μm larger than the particle size D50 of the product particles in step (1), so that the obtained positive electrode material coated with a composite oxide is adaptively changed.

[0081] Example 6

[0082] This embodiment provides a positive electrode material coated with a composite oxide. The positive electrode material coated with a composite oxide is the same as that in Example 1 except that in its preparation method, the aluminum salt solution in step (2) is replaced with a zirconium sulfate solution at an equal concentration to change the adaptability of the obtained positive electrode material coated with a composite oxide.

[0083] Example 7

[0084] This embodiment provides a positive electrode material coated with a composite oxide. The positive electrode material coated with a composite oxide is the same as that in Example 1, except that in the preparation method, the zinc salt solution in step (2) is replaced with a copper sulfate solution at an equal concentration to change the adaptability of the obtained positive electrode material coated with a composite oxide.

[0085] Example 8

[0086] This embodiment provides a positive electrode material coated with a composite oxide. The positive electrode material coated with the composite oxide is the same as that in Example 1, except that in the preparation method, the concentration of the zinc salt solution is adaptively changed so that the molar ratio of zinc ions in the zinc salt solution to aluminum ions in the aluminum salt solution is 0.5:1, thereby adaptively changing the obtained positive electrode material coated with the composite oxide.

[0087] Example 9

[0088] This embodiment provides a positive electrode material coated with a composite oxide. The positive electrode material coated with the composite oxide is the same as that in Example 1, except that in its preparation method, the concentration of the zinc salt solution is adaptively changed so that the molar ratio of zinc ions in the zinc salt solution to aluminum ions in the aluminum salt solution is 5:1, thereby adaptively changing the obtained positive electrode material coated with the composite oxide.

[0089] Example 10

[0090] This embodiment provides a positive electrode material coated with a composite oxide. The positive electrode material coated with the composite oxide is the same as that in Example 1 except that step (2) is not performed in the preparation method. Instead, the core precursor material described in step (1) is subjected to the primary sintering and secondary sintering of step (3) with a sodium source to obtain a sintered material. The obtained sintered material is mixed with aluminum oxide and zinc oxide and sintered at 500°C for 5 hours to make the obtained positive electrode material coated with the composite oxide adaptable. The addition amount of aluminum oxide and zinc oxide can keep the thickness of the coating layer the same as that in Example 1.

[0091] Comparative Example 1

[0092] This comparative example provides a positive electrode material coated with a composite oxide. The positive electrode material coated with a composite oxide is the same as Example 1 except that step (2) is not performed in the preparation method to adapt the obtained positive electrode material coated with a composite oxide.

[0093] Comparative Example 2

[0094] This comparative example provides a positive electrode material coated with a composite oxide. The positive electrode material coated with the composite oxide is the same as that in Example 1 except that in its preparation method, no M salt solution is added during the coprecipitation reaction in step (1), which causes the adaptability of the obtained positive electrode material coated with the composite oxide to change.

[0095] The positive electrode materials obtained in the above embodiments and comparative examples were used as the positive electrode main material, and the metal sodium sheet was used as the negative electrode, and they were assembled into CR2032 button batteries, using 1 mol / L NaClO4 solution as the electrolyte and a glass fiber membrane with a diameter of 16 mm as the separator. The electrochemical performance test was carried out by cycling 100 times at a current density of 1 C in the voltage range of 2-4 V.

[0096] The test results are shown in the following table:

[0097] Table 1

[0098] From the above table we can see that:

[0099] It can be seen from Example 1 and Comparative Examples 1-2 that the doping and coating of the positive electrode material described in the present application can significantly improve the performance of the sodium ion battery; it can be seen from Example 1 and Examples 4-7 that the thickness of the coating layer and the selection of the metal type in the coating layer will affect the function of the coating layer, thereby affecting the battery performance; it can be seen from Example 1 and Examples 8-9 that the molar ratio of aluminum and zinc in the coating layer will affect the coordination of the two, thereby affecting the battery performance; it can be seen from Example 1 and Example 10 that the present application preferably co-precipitates the coated metal hydroxide and then sintering it, which can generate a uniformly coated aluminum oxide zinc coating in situ, thereby improving the battery performance.

[0100] In summary, the present application provides a positive electrode material coated with a composite oxide, a preparation method and an application thereof. By coating the composite oxide, the positive electrode material significantly improves the conductivity and stability of the positive electrode material, reduces the contact between the positive electrode material and the electrolyte, inhibits the occurrence of side reactions, and improves the cycle performance of the material.

[0101] The above description is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Those skilled in the art should understand that any changes or replacements that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application fall within the protection scope and disclosure scope of the present application.

Claims

1. A cathode material coated with a composite oxide, comprising a core and a coating layer on the surface of the core, and the chemical general formula of the core is Na b Ni x Fe y Mn z M 1-x-y-z O 2 , Among them, 0.4 ≤ b ≤ 1.2, 0.10 ≤ x ≤ 0.50, 0.10 ≤ y ≤ 0.50, 0.10 ≤ z ≤ 0.50, M includes any one or at least two combinations of Li, Cu, Al, Mg, Zn, Sn, Ti, Zr, Sr, Sb, Nb, Ba, Cr, Mo, Y, Ca, Rb, Cs, Ce, Ta, V, Sc, B, V, Co, La, Ru or W, the coating layer includes a composite oxide, and the composite oxide includes more than two metal elements.

2. The cathode material coated with a composite oxide according to claim 1, Among them, the composite oxide includes aluminum zinc oxide; Optionally, the particle size D50 of the core is 3 - 14 μm; Optionally, the thickness of the coating layer is 0.2 - 2 μm.

3. A method for preparing the cathode material coated with a composite oxide according to claim 1 or 2, comprising the following steps: (1) Mix a nickel-iron-manganese metal salt solution, an M salt solution, a precipitant solution and a complexing agent solution, and carry out a coprecipitation reaction to obtain a core precursor material; (2) After obtaining the core precursor material in step (1), stop feeding the nickel-iron-manganese metal salt solution and the M salt solution, introduce a coating source solution, and continue to carry out a coprecipitation reaction between the coating source solution and the precipitant solution and the complexing agent solution to obtain a cathode precursor material; the coating source solution includes more than two metal elements; (3) Mix and sinter a sodium source with the cathode precursor material in step (2) to obtain the cathode material coated with a composite oxide.

4. The preparation method according to claim 3, Among them, in the nickel-iron-manganese metal salt solution in step (1), the total metal ion concentration is 0.6 - 5 mol / L; Optionally, the concentration of the M salt solution in step (1) is 0.05 - 2 mol / L; Optionally, the concentration of the precipitant solution in step (1) is 1 - 10 mol / L, and the concentration of the complexing agent solution is 2 - 15 mol / L.

5. The preparation method according to claim 3 or 4, Among them, Feed the nickel-iron-manganese metal salt solution, the M salt solution, the precipitant solution and the complexing agent solution in step (1) into the bottom liquid in parallel and carry out a coprecipitation reaction; Optionally, the pH of the bottom liquid is 9 - 12; Optionally, the temperature of the coprecipitation reaction in step (1) is 20 - 80 °C, and the pH is maintained within the range of 7 - 11; Optionally, when the particle size D50 of the product particles in the coprecipitation reaction in step (1) reaches 3 - 14 μm, stop the reaction to obtain a core precursor material.

6. The preparation method according to any one of claims 3 - 5, Among them, the coating source solution in step (2) includes an aluminum salt solution and a zinc salt solution; Optionally, the molar ratio of zinc ions in the zinc salt solution to aluminum ions in the aluminum salt solution is (1 - 4):1; Optionally, the concentration of the zinc salt solution is 0.5 - 4 mol / L, and the concentration of the aluminum salt solution is 0.1 - 2.5 mol / L.

7. The preparation method according to any one of claims 3 - 6, Among them, After the D50 of the product particles in the coprecipitation reaction described in step (2) increases by 0.2 - 2 μm compared to the D50 of the product particles in step (1), the reaction is stopped; Optionally, the temperature of the coprecipitation reaction described in step (2) is 30 - 70 °C, and the pH is maintained within the range of 7 - 10.

8. The preparation method according to any one of claims 3 - 7, wherein, The sintering in step (3) includes primary sintering and secondary sintering carried out in sequence. The temperature of the primary sintering is 450 - 600 °C, and the time is 4 - 6 h. The temperature of the secondary sintering is 750 - 1200 °C, and the time is 10 - 25 h; Optionally, the sintering in step (3) is carried out in an oxygen atmosphere.

9. The preparation method according to any one of claims 3 - 8, wherein, The preparation method includes the following steps: (1) The nickel - iron - manganese metal salt solution, M salt solution, precipitant solution, and complexing agent solution are fed in parallel into a bottom solution with a pH of 9 - 12 for coprecipitation reaction. The temperature of the coprecipitation reaction is 20 - 80 °C, and the pH is maintained within the range of 7 - 11. When the D50 of the product particles in the coprecipitation reaction reaches 3 - 14 μm, the reaction is stopped, and a core precursor material is obtained; In the nickel - iron - manganese metal salt solution, the total metal ion concentration is 0.6 - 5 mol / L, the concentration of the M salt solution is 0.05 - 2 mol / L, the concentration of the precipitant solution is 1 - 10 mol / L, and the concentration of the complexing agent solution is 2 - 15 mol / L; (2) After obtaining the core precursor material in step (1), the feeding of the nickel - iron - manganese metal salt solution and M salt solution is stopped, and an aluminum salt solution and a zinc salt solution are fed in. The aluminum salt solution and the zinc salt solution continue to carry out coprecipitation reaction with the precipitant solution and the complexing agent solution. The temperature of the coprecipitation reaction is 30 - 70 °C, and the pH is maintained within the range of 7 - 10. After the D50 of the product particles in the coprecipitation reaction increases by 0.2 - 2 μm compared to the D50 of the product particles in step (1), the reaction is stopped, and a cathode precursor material is obtained; The concentration of the zinc salt solution is 0.5 - 4 mol / L, and the concentration of the aluminum salt solution is 0.1 - 2.5 mol / L; (3) A sodium source is mixed with the cathode precursor material in step (2), and then, in an oxygen atmosphere, it is sintered at a temperature of 450 - 600 °C for 4 - 6 h for the first time, and then sintered at a temperature of 750 - 1200 °C for 10 - 25 h for the second time to obtain the cathode material of the coated composite oxide.

10. A sodium - ion battery comprising a cathode material including the coated composite oxide according to claim 1 or 2.

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